1. Field of the Invention
This invention involves traffic signal controllers and more particularly a radio-activated traffic signal controller activated by an emergency vehicle for changing the mode of operation of the traffic signal so as to stop traffic in all directions as the emergency vehicle approaches the intersection.
2. Description of the Prior Art
Remote control of traffic signal systems by emergency vehicles in order to facilitate movement of emergency vehicles through traffic and reduce the hazard to the emergency vehicle and other traffic when emergency runs are being carried out has long been seen as a desirable feature of traffic signals. In most of these systems a radio, ultrasonic, or proximity-sensing-arrangement of some sort has been utilized to trigger an emergency mode for the traffic light controller, typically turning all of the lights red or alternatively the lights in the transverse direction to the approach of the vehicle red to facilitate movement of the emergency vehicles through the intersection.
Some variations of this concept have been proposed such as that disclosed in U.S. Pat. No. 3,257,641 which discloses a radio-activated system which triggers an emergency siren and an emergency light in conjunction with activating all of the red lights, as long as the emergency vehicle is within transmission range.
In U.S. Pat. No. 3,881,169 various permutations of this concept are proposed which includes activating all of the red lights in the signals to a flashing condition.
In another variation the cross street is activated to a blinking red condition, while the street down which the emergency vehicle is traveling has its amber lights activated in a flashing condition.
In U.S. Pat. No. 2,881,409, a system is disclosed in which the traffic signal is activated so as to initially flash yellow, then to a steady red, both in the cross street direction.
In U.S. Pat. No. 3,114,127, the radio-activated controller briefly flashes all of the lights red, while sequencing the normal traffic signal controls to obtain the right sense of the traffic signals to conform with the direction of approach of the emergency vehicle. At this point, the lights are maintained in this condition until the emergency vehicle passes.
Other typical systems are disclosed in U.S. Pat. Nos. 3,636,507, 2,203,871 and 3,209,325.
However, no such system has enjoyed widespread acceptance. It is felt that an overriding concern in the design of any such system is that the cost be held to a minimum and that this be done without compromising the reliability of the system, since traffic lights must be highly reliable to keep maintenance costs within reason and to avoid the resultant disruption of traffic which would result from the failure of the traffic signal to operate properly.
The systems described in these patents can all be characterized as being relatively complex and costly in design with undue elaborateness in the circuitry and in the control modes which would contribute, in no small part, to relatively high manufacturing installation costs and which would contribute to the maintenance problems described.
It is therefore an object of the present invention to provide such an emergency vehicle activated traffic light controller which is simple in design, while performing the essential functions required of such a device. In connection with this object it is also an object of the present invention to provide such a design which is readily incorporatable into the traffic signal control systems presently in use.